Looking at sails

Solving sail and hull design problems is usually a matter of compromise and weighting. Every rig has its advantages and drawbacks and in eclectically combining the best of all, the result is often a mess which doesn’t have any of the advantages.

Often, a rig is great in that context, in that size, on that craft. Try to transfer it and it doesn’t work, e.g. the windsurfer foil. On a larger boat, the mast is not stiff enough for the weight of sail but what if a wingmast were to be the leading edge [only more curved]:

Tom Speer did a lot of work on partial wings and discovered that 10-15% of the total fore and aft length was a good size – not, 20%, not 50% – and that the only thing better was 100%:

As I’m interested in the simplest and cheapest cruising rig, the full wingsail is not only right out of the ballpark, costwise but its advantage in sailing, i.e. it will move over a large range of angles of attack, whereas a conventional sail must have the angle “just so”, is a racing advantage but a cruising nightmare.

What though if you had a 10% wing as your leading edge and ran a lateen sail like a crab claw? So you’d use a configuration like Gary Dierking’s, with a stubby mast set into the keel, not needing stays, then the two long “yards” would hang from that:

Where he uses straight spars, we’d use curved, more in a crab claw shape:

… but would opt to lose the crab claw efficiency for wingmast efficiency and replace the leading spar with the wing, getting back more to the windsurfer shape [at the top]. That allows for greater area and pulls the centre of effort lower [no huge amounts of sail waving about up in the air].

Now, if two of those were to be used – a larger at the front and a smaller at the back, mainly for navigational aid – picture this below with the lower spars down further towards the deck:

… then it needs one more embellishment. You see, if you drop the foot of the sail closer to the deck but it extends behind the rear mast, there is the issue of how to get the boom over to the other side without lifting it high and dropping it again each time.

My solution is not to have a boom but a heavy boltrope instead, not unlike those used to tie up ships, sewn or tied along the foot. It’s stiff enough to hold its shape as long as the sheet [line pulling the sail in], leads aft and down, plus a traveller system is used:

Not state of the art like this but one using two cables from the centre hull out to the amas. So yes, I neglected to mention that this will only work on a trimaran configuration. And that’s only for the mainsail up front. The smaller sail behind would have a boom which would swing out from the one point at the stern and tack itself across.

The advantage over the gaff rig is less windage and a clean leading edge, over the lug in that there’s no loose leading edge sagging or flapping about, the rig is more rigid and yet allows the sail its natural curve. It’s a much simpler rig than a modern bermudan, in terms of running rigging, it carries the centre of effort far lower, the “hockey stick” head allows a more square shape downwind and the wing can be dropped to the deck quickly – within seconds.

The N1 criticism of the crab claw though [or sails with two equi-length spars] is that it can’t be reefed [sail reduced]. This one can and the bolt-rope gets over the disadvantage of loose-footed sails -difficult to reef. The crab claw uses brail lines which when tautened, ruin the shape of the sail and therefore depower it, an advantage at sea. So our sail would have these too, also doubling as lazy jacks:

The disadvantage of the modern bermudan is that ultratall mast, needing bracing, invoking huge pressures on rig and boat and in a storm, that tall mast is swaying about up there, even without sail. With this compromise design of mine, you get none of that, you don’t get the stresses but you get the efficiency in good winds.

Why haven’t people done this yet? The answer is that people tend not to like hybrids – they tend to use the rigs which are common in that geographical area and look to resale value. As I have no scanner, I can’t show my sail profile to you but imagine a cross between the above, blended into a rough crab claw, a lifting rig – also not unlike a huge genoa:

Now picture the leading edge not concave, like this but convex, led by a wing, which in turn hangs behind a stubby mast. The short mast itself has windage but the wing hangs downwind and has clean air on its outer or lee side.

It would most certainly work but your obvious question would be – why on a cruising craft? The answer is that such a sail has an efficiency of 1.5 or thereabouts on a reach over a conventional sail and about evens upwind – so less area required, less sailcloth overall. Ease of handling onboard – halyard and sheet only, via a winch and only one major sail needing attention – the mizzen behind is small and virtually takes care of itself.

On a 37 foot boat, the 409 sq feet is not to large to handle, particularly when the wing simply lowers beside the boltrope and is tied down in a storm. The expense is not in the sail but in the wing and that would take some construction but as you’re saving on labour elsewhere, it might as well go into the wing. Also, if it did break, it could be lowered to the deck and repaired there with metal “splints” whilst a storm jib takes its place.

I can only see this working on a trimaran, not a cat because it requires rigidity at the three corners but if you did build a tri, then this would be your most efficient, for the lowest stresses and easiest handling of any rig used by sailors.

Now I just need a spare £20 000 which, as yachtsmen will tell you, is chickenfeed these days although admittedly, not for me.

And the hull shape? I quite like the Scottish/Nordic double-enders. Picture this at 37 feet, with low cabin and the rig mentioned above:

By the way, that would be the construction method too – clinker or lapstrake.